Shares of Potbelly (PBPB) surged 135% on its initial public offering Friday, making it the hottest IPO debut of 2013 since Noodles (NDLS). Potbelly stock was priced at $14, above the expected the range, and immediately doubled when it began trading at 10 a.m. ET. Near midday Potbelly shot up 136% in the stock market today. The IPO raised $105 million, more than 25% above expectations. Potbelly is a fast-casual restaurant chain that sells